1. Field of the Invention
The present invention relates to an electro-conductive member, a process cartridge, and an electrophotographic apparatus.
2. Description of the Related Art
In an electrophotographic image-forming apparatus, an electro-conductive member has been used in various fields such as a charging roller, a developing roller, and a transfer roller. The electrical resistivity of such an electro-conductive member preferably falls within the range of 103 to 1010Ω. Accordingly, the conductivity of an electro-conductive layer which the electro-conductive member includes has been adjusted with an electro-conductive agent. Here, the electro-conductive agents are roughly classified into an electronic conductive agent typified by carbon black and an ionic conductive agent such as a quaternary ammonium salt compound. Those conductive agents each have an advantage and a disadvantage.
An electro-conductive layer that has been made conductivity with the electronic conductive agent such as carbon black shows a small change in electrical resistivity with a use environment. In addition, the electronic conductive agent hardly bleeds to the surface of the electro-conductive layer, and hence there is a small possibility that the agent contaminates the surface of a member on which an electro-conductive member including such an electro-conductive layer abuts, e.g., an electrophotographic photosensitive member (hereinafter referred to as “photosensitive member”). However, it is difficult to uniformly disperse the electronic conductive agent in a binder resin and hence the electronic conductive agent is liable to agglomerate in the electro-conductive layer. Accordingly, local unevenness of the electrical resistivity may occur in the electro-conductive layer.
On the other hand, in the case of an electro-conductive layer that has been made conductivity with the ionic conductive agent, the ionic conductive agent is uniformly dispersed in a binder resin as compared with the electronic conductive agent. Accordingly, local resistance unevenness hardly occurs in the electro-conductive layer. However, the ion-conducting performance of the ionic conductive agent is susceptible to the amount of moisture in the binder resin under a use environment. Accordingly, the electrical resistivity of the electro-conductive layer that has been made conductivity with the ionic conductive agent increases under a low-temperature, low-humidity environment (having a temperature of 15° C. and a relative humidity of 10%) (hereinafter, sometimes referred to as “L/L environment”), and reduces under a high-temperature, high-humidity environment (having a temperature of 30° C. and a relative humidity of 80%) (hereinafter sometimes referred to as “H/H environment”). That is, the electro-conductive layer involves a problem in that the environmental dependence of its electrical resistivity is large.
Further, when a direct-current voltage is applied to an electro-conductive member including the electro-conductive layer that has been made conductivity with the ionic conductive agent over a long time period, the following tendency has been observed. A cation and anion constituting the ionic conductive agent are polarized in the electro-conductive layer, an ion density in the electro-conductive layer reduces, and the electrical resistivity of the electro-conductive layer gradually increases.
Japanese Patent Application Laid-Open No. 2004-184512 discloses an electrophotographic equipment member in which the voltage dependence and environmental dependence of the resistance have been suppressed. Specifically, the literature proposes that the electrophotographic equipment member be formed with a semiconductive composition containing a binder polymer having, in its molecular structure, at least one of a sulfonic group and a sulfonic acid metal salt structure, and an electro-conductive polymer having, in its molecular structure, a surfactant structure formed with a surfactant having a sulfonic group.